This invention relates to fluid collection devices and more particularly to blood collection devices having means for partitioning the lighter and heavier phases of blood.
In the testing of blood samples, whole blood is usually drawn into an evacuated tube and the tube placed in a centrifuge for separating the lighter and heavier phases so that the individual phases may be isolated and tested. Many different types of phase partitioning devices which provide a barrier or seal between the separated phases have been used or proposed for the purpose of allowing the lighter phase to be decanted or poured into a transfer tube free of cells, or to enable the two phases to remain in the collection tube without intermixing during shipment to a laboratory where the lighter phase is removed and subjected to analysis.
In U.S. Pat. No. 3,852,194 and U.S. Pat. No. 3,780,935, gel-like materials, such as a silicone material including a silicone fluid and silica powders, is disposed in a collection tube, the gel-like material having a specific gravity between that of the lighter phase and that of the heavier phase so that it flows to the interface of the two phases and forms a partition between them. These devices generally require a relatively large amount of gel-like material, and in addition to the relatively high cost of the material, a relatively large surface area of the material is in contact with the blood components before, during, and after centrifugation. This relatively large surface area of contact tends to increase the danger of interaction between the gel-like material and lighter blood phase which is to be analyzed. For example, collection tubes are used that employ silicone gel-like materials which produce oil in the lighter phase which tends to clog and restrict the flow of fluid in the tubing of blood analyzing equipment, especially in automatic blood analyzers. In U.S. Pat. 3,852,194 there is also disclosed a relatively complicated arrangement which includes a spool member, which may be made of rubber, having a hole through it and which has a wiper for sealing contact with the inner wall of the tube. The spool moves toward the closed end of the tube while the gel-like material moves toward the stopper and closes the hole in the spool member upon separation of the phases.
In U.S. Pat. No. 3,909,419, a plasma separator is used wherein a pair of cylinders are disposed in the container and a plurality of micro encapsulated beads of gelatin are disposed between the cylinders. The specific gravities of the two cylinders and the gelatin beads are such that, by increasing the speed of the centrifuge after the phases have been separated, the cylinders move toward each other and rupture the encapsulated beads to cause the gelatin to form a seal between the cylinders and inner wall of the container at a location between the two phases. This arrangement is relatively expensive since it requires the manufacture of encapsulated beads and also requires centrifugation at two different speeds.